Final answer:
Investigation of a tax problem in a closed-fact situation means that the client's transactions have occurred and tax laws must be applied to resolve issues.
Step-by-step explanation:
Investigation of a tax problem involving a closed−fact situation means that C. the client's transactions have already occurred and the tax questions must now be resolved.
In such scenarios, all relevant financial transactions and events have happened, and the role of a tax professional is to apply existing tax laws to those facts to determine the client's tax liability or resolve any issues arising from those transactions. This type of investigation is retrospective, as it looks at completed actions rather than planning for the future or preparing for upcoming tax filings.